共查询到20条相似文献,搜索用时 26 毫秒
1.
Wearthering steels treated with and without zinc phosphate solution were exposed to atmosphere for 15 years and rust layers produced on the steels were analysed by scattering Mössbauer spectrometry (CEMS and XMS). γ-FeOOH, fine α-FeOOH, 5Fe 2O 3·9H 2O, γ-Fe 2O 3 and Fe 3O 4 were identified to be present in the rust formed on the steel without phosphate coating. Large particles of γ-Fe 2O 3 and Fe 3O 4 formed on the uncoated steel exposed to atmosphere in a position facing north on vertical plane. The layer structure of rust was affected by the position. The thin rust layer formed on the phosphate + carylite resin coated steel was considered to consist of γ-FeOOH, fine α-FeOOH, and fine γ-Fe 2O 3. 相似文献
2.
By using a KNO 3-aging ferrous hydroxide gel method, Fe 3O 4 particles with sizes ranging from 35 to 1500 nm were synthesized. The particles were covered with a silica coating to form Fe 3O 4-SiO 2 core-shell structures by using the improved conventional Stöber polycondensation method. The thickness of the SiO 2 covering on magnetite particles surface varies from 10 to 20 nm. The morphology, size and composition of the particles were determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The particles with and without coating with SiO 2 were pressed into slices with an oil press at 10 MPa. Subsequently, the coercive forces HC of the particles were measured by VSM at room temperature, and the critical size for a single domain was estimated. The shape of the particles is basically spherical when the size is smaller than 800 nm, while it is hexagonal for larger particles. The HC of Fe 3O 4-SiO 2 core-shell structure was larger than that of the uncoated Fe 3O 4 particles by 20%, which was explained to be due to the reduction of inter-particle magnetostatic interaction, supported by an agreement with the packing factor. The dependence of HC on magnetic particle size could be explained and fitted by the Heewell-Knozam stacking density equation and object-oriented micromagnetic computing framework (OOMMF) micromagnetic software. the results agree well with the experimental data. 相似文献
3.
Fe 3O 4-based heterostructures, including Fe 3O 4/MgO/Fe 3O 4, Fe 3O 4/MgO/Si and Fe 3O 4/SiO 2/Si, were fabricated by magnetron sputtering to investigate the perpendicular-to-plane magneto-transport properties. In the Fe 3O 4/MgO/Fe 3O 4 and Fe 3O 4/MgO/Si heterostructures, the typical magneto-transport properties of single Fe 3O 4 films, such as negative magnetoresistance (MR) and extreme values of MR− T curves at 120 K, were observed, suggesting that the spin polarization of conducting electrons conserves through MgO barrier. MR in the Fe 3O 4/MgO/Fe 3O 4 heterostructure is larger than that in the Fe 3O 4/MgO/Si heterostructure, because the spin of electrons is disturbed in the depletion layer of Si and the SiO 2 layer introduced by Fe 3O 4/MgO growth. The Fe 3O 4/SiO 2/Si heterostructure has a positive MR of 2% at 120 K, which may originate from the scattering of conducting electrons in amorphous SiO 2 and the spin polarization reversal at the Fe 3O 4/SiO 2 interface. 相似文献
4.
The method of obtaining nanoclusters α-Fe2O3 in the pores of monodisperse spherical particles of mesoporous silica (mSiO2) by a single impregnation of the pores with a melt of crystalline hydrate of ferric nitrate and its subsequent thermal destruction has been proposed. Fe3O4 nanoclusters are synthesized from α-Fe2O3 in the pores by reducing in thermodynamically equilibrium conditions. Then particles containing Fe3O4 were annealed in oxygen for the conversion of Fe3O4 back to α-Fe2O3. In the result, the particles with the structure of the core-shell mSiO2/Fe3O4@mSiO2/α-Fe2O3 are obtained. The composition and structure of synthesized materials as well as the field dependence of the magnetic moment on the magnetic field strength have been investigated. 相似文献
5.
The corrosion products on steels exposed at two sites in Campeche, México and one site at Kure Beach, USA, have been investigated to determine the extent to which different marine conditions and exposure times control the oxide formation. The corroded coupons were analyzed by Mössbauer, Raman and infrared spectroscopy as well as X‐ray diffraction, in order to completely identify the oxides and map their location in the corrosion coating. The coating compositions were determined by Mössbauer spectroscopy using a new parameter, the relative recoilless fraction ( F-value) which gives the atomic fraction of iron in each oxide phase from the Mössbauer sub‐spectral areas. For short exposure times, less than three months, an amorphous oxyhydroxide was detected after which a predominance of lepidocrocite (γ-FeOOH), and akaganeite (β-FeOOH) were observed in the corrosion coatings with the fraction of the later phase increasing at sites with higher atmospheric chloride concentrations. The analysis also showed that small clusters of magnetite (Fe 3O 4), and maghemite (γ(Fe 2O 3), were seen in the micro-Raman spectra but were not always identified by Mössbauer spectroscopy. For longer exposure times, goethite (α-FeOOH), was also identified but little or no β-FeOOH was observed. It was determined by the Raman analysis that the corrosion products generally consisted of inner and outer layers. The protective layer, which acted as a barrier to slow further corrosion, consisted of the α-FeOOH and nano-sized γ-Fe 2O 3 phases and corresponded to the inner layer close to the steel substrate. The outer layer was formed from high γ-FeOOH and low α-FeOOH concentrations. 相似文献
6.
The Verwey transition in Fe 3O 4 nanoparticles with a mean diameter of 6.3 nm is suppressed after capping the particles with a 3.5 nm thick shell of SiO 2. By X‐ray absorption spectroscopy and its associated X‐ray magnetic circular dichroism this suppression can be correlated to localized Fe 2+ states and a reduced double exchange visible in different site‐specific magnetization behavior in high magnetic fields. The results are discussed in terms of charge trapping at defects in the Fe 3O 4/ SiO 2 interface and the consequent difficulties in the formation of the common phases of Fe 3O 4. By comparison to X‐ray absorption spectra of bare Fe 3O 4 nanoparticles in course of the Verwey transition, particular changes in the spectral shape could be correlated to changes in the number of unoccupied d states for Fe ions at different lattice sites. These findings are supported by density functional theory calculations. 相似文献
7.
The surface structure of the iron oxide nanoparticles obtained by the co-precipitation method has been investigated, and a thin layer of α-FeOOH absorbed on surface of the nanoparticle is confirmed by analyses of Fourier transform infrared (FTIR), X-ray photoelectron spectra (XPS) and surface photovoltage spectroscopy (SPS). After annealed at 400 °C, the α-FeOOH can be converted to γ-Fe 2O 3. The simple-annealed procedure resulted in the formation of Fe 3O 4@γ-Fe 2O 3 core/shell structure with improved stability and a higher magnetic saturation value, and also the simple method can be used to obtain core/shell structure in other similar system. 相似文献
8.
Samples of the iron oxides Fe 0.94O, Fe 3O 4, Fe 2O 3, and Fe 2SiO 4 were prepared by high temperature equilibration in controlled gas atmospheres. The samples were fractured in vacuum and high resolution XPS spectra of the fractured surfaces were measured. The peak positions and peak shape parameters of Fe 3p for Fe 2+ and Fe 3+ were derived from the Fe 3p XPS spectra of the standard samples of 2FeO·SiO 2 and Fe 2O 3, respectively. Using these parameters, the Fe 3p peaks of Fe 3O 4 and Fe 1−yO are analysed. The results indicate that high resolution XPS techniques can be used to determine the Fe 2+/Fe 3+ ratios in metal oxides. The technique has the potential for application to other transition metal oxide systems. 相似文献
9.
Magnetic measurements have been performed on 40-nm sphere-like Fe 3 − δO 4 ( δ=0.043) nanoparticles using a Quantum Design vibrating sample magnetometer. Coating Fe 3 − δO 4 nanoparticles with SiO 2 effectively eliminates magnetic interparticle interactions so that the coercive field HC in the high-temperature range between 300 K and the Curie temperature (855 K) can be well fitted by an expression for noninteracting randomly oriented single-domain particles. From the fitting parameters, the effective anisotropy constant K is found to be (1.38±0.11)× 105 erg/cm 3, which is very close to the bulk magnetocrystalline anisotropy constant of 1.35× 105 erg/cm 3. Moreover, the inferred mean particle diameter from the fitting parameters is in quantitative agreement with that determined from transmission electron microscope. Such a quantitative agreement between data and theory suggests that the ensemble of our SiO 2-coated sphere-like Fe 3 − δO 4 nanoparticles represents a good system of noninteracting randomly-oriented single-domain particles. 相似文献
10.
A novel method is described for the preparation of superparamagnetic mesoporous maghemite (γ-Fe 2O 3)/silica (SiO 2) composite microspheres to allow rapid magnetic separation of DNA from biological samples. With magnetite (Fe 3O 4) and silica nanoparticles as starting materials, such microspheres were synthesized by the following two consecutive steps: (1) formation of monodispersed organic/inorganic hybrid microspheres through urea-formaldedyde (UF) polymerization and (2) removal of the organic template and phase transformation of Fe 3O 4 to γ-Fe 2O 3 by calcination at elevated temperatures. The as-synthesized particles obtained by heating at temperature 300 °C feature spherical shape and uniform particle size ( dparticle=1.72 μm), high saturation magnetization ( Ms=17.22 emu/g), superparamagnetism ( Mr/ Ms=0.023), high surface area ( SBET=240 m 2/g), and mesoporosity ( dpore=6.62 nm). The composite microsphere consists of interlocked amorphous SiO 2 nanoparticles, in which cubic γ-Fe 2O 3 nanocrystals are homogeneously dispersed and thermally stable against γ- to α-phase transformation at temperatures up to 600 °C. With the exposed iron oxide nanoparticles coated with a thin layer of silica shell, the magnetic microspheres were used as a solid-phase adsorbent for rapid extraction of genomic DNA from plant samples. The results show that the DNA templates isolated from pea and green pepper displayed single bands with molecular weights greater than 8 kb and A260/ A280 values of 1.60-1.72. The PCR amplification of a fragment encoding the endogenous chloroplast ndhB gene confirmed that the DNA templates obtained were inhibitor-free and amenable to sensitive amplification-based DNA technologies. 相似文献
11.
A relationship between methylene blue (MB) decomposition ability under visible light and local structure of xFe 2O 3·(100- x)SiO 2 glass abbreviated as xFS prepared by sol-gel method was investigated by 57Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD) and ultraviolet-visible light absorption spectroscopy (UV-Vis). Mössbauer spectra of xFS glass with x of 10, 30 and 50 annealed at 1000 °C for 3 h were mainly composed of a paramagnetic doublet due to fayalite (Fe 2SiO 4), and magnetic sextets due to magnetite (Fe 3O 4) or hematite ( α-Fe 2O 3). The absorption area ( A) of α-Fe 2O 3 gradually increased from 0.0 to 10.3 and 100 % with the increasing Fe 2O 3 content ( x) of annealed xFS glass. A leaching test performed by 20 mL of MB aqueous solution and 40 mg of annealed 50FS glass showed that MB concentration decreased from 16.2 to 4.7 μmol L ?1 after 2 h with the first order rate constant of 1.8 × 10 ?4 s ?1. These results prove that annealed iron silicate glass containing α-Fe 2O 3 can decompose MB effectively under visible light irradiation. 相似文献
12.
Core–shell Cu/γ‐Fe 2O 3@C and yolk–shell‐structured Cu/Fe@γ‐Fe 2O 3@C particles are prepared by a facile synthesis method using copper oxide as template particles, resorcinol‐formaldehyde as the carbon precursor, and iron nitrate solution as the iron source via pyrolysis. With increasing carbonization temperature and time, solid γ‐Fe 2O 3 cores are formed and then transformed into Fe@γ‐Fe 2O 3 yolk–shell‐structured particles via Ostwald ripening under nitrogen gas flow. The composition variations are studied, and the formation mechanism is proposed for the generation of the hollow and yolk–shell‐structured metal and metal oxides. Moreover, highly graphitic carbons can be obtained by etching the metal and metal oxide nanoparticles through an acid treatment. The electrocatalytic activity for oxygen reduction reaction is investigated on Cu/γ‐Fe 2O 3@C, Cu/Fe@γ‐Fe 2O 3@C, and graphitic carbons, indicating comparable or even superior performance to other Fe‐based nanocatalysts. 相似文献
13.
Stable silicon oil based ferrofluid was prepared in the present investigation. Silicon oil surfactant ethoxy terminated polydimethylsiloxane was used to modify the Fe 3O 4 nanoparticles. The Fe 3O 4 nanoparticles were firstly coated with a SiO 2 layer by the hydrolysis of tetraethoxysilane. Then using the active hydroxyl groups on the surface of the SiO 2, silicon oil surfactant was covalently grafted onto the Fe 3O 4 nanoparticles surface. The ethoxy terminated polydimethylsiloxane has similar molecular chain structure and good compatibility with that of the carrier liquid, thus ensuring stable dispersion of modified Fe 3O 4 in the carrier silicon oil. The interaction between Fe 3O 4 and the modifier was characterized by IR and XPS. The crystal structure and the magnetic properties of the Fe 3O 4 nanoparticles were determined by XRD and VSM, respectively. The size and morphology of the particles were observed using TEM. The properties of the silicon oil based ferrofluid were characterized by Gouy magnetic balance. The results indicated that the ferrofluid had high magnetism and good stability. The rheological properties and thermostability of the ferrofluid were also investigated. 相似文献
14.
Nano-magnetic Fe 3O 4 particles coated with silica are synthesized. The study of structural and magnetic properties was carried out using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometer (VSM) techniques. The VSM results show that these kinds of composite particles exhibit superparamagnetic behavior with zero coercivity and remanence. The magnetic spheroid alumina carriers containing these magnetic composite particles were prepared by an internal gelation process. The SiO 2 coatings prevent the reaction between Fe 3O 4 and Al 2O 3 during the sintering process and maintain the superparamagnetic behavior of the catalyst carriers. 相似文献
15.
For fundamental studies of the atmospheric corrosion of steel, it is useful to identify the iron oxide phases present in rust
layers. The nine iron oxide phases, iron hydroxide (Fe(OH) 2), iron trihydroxide (Fe(OH) 3), goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), feroxyhite (δ-FeOOH), hematite (α-Fe 2O 3), maghemite (γ-Fe 2O 3) and magnetite (Fe 3O 4) are among those which have been reported to be present in the corrosion coatings on steel. Each iron oxide phase is uniquely
characterized by different hyperfine parameters from M?ssbauer analysis, at temperatures of 300K, 77K and 4K. Many of these
oxide phases can also be identified by use of Raman spectroscopy. The relative fraction of each iron oxide can be accurately
determined from the M?ssbauer subspectral area and recoil-free fraction of each phase. The different M?ssbauer geometries
also provide some depth dependent phase identification for corrosion layers present on the steel substrate. Micro-Raman spectroscopy
can be used to uniquely identify each iron oxide phase to a high spatial resolution of about 1 μm.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
The effect of anions such as Cl −, SO 42−, and HPO 42− on the phase stability of FeOOH (α or γ) during precipitation is investigated. Oxidation of Fe(OH) 2· xH 2O from FeCl 2 solution with high Cl − concentration ([Cl −]/[Fe]= RCl≥8) or (NH 4) 2Fe(SO 4) 2 (FAS) with [HPO 42−]/[Fe]= RP≥0.02 yields phase-pure γ-FeOOH. In the medium ranges of RCl and RP, mixed phases of α-FeOOH and γ-FeOOH are obtained. Replacement of OH − by Cl − with the bridging cations or strongly bonded HPO 42− ions in the matrix of the intermediate phase (Fe x2+Fe y3+(OH) 2x+2y−nz· xH 2O(A) zn−, where A is anions such as Cl −, SO 42−, HPO 42−, etc.), promoted the lower density γ-FeOOH. However, the particles are less developed and have poor crystallinity as evidenced from transmission electron microscope and thermogravimetry-differential thermal analysis of the precipitates. Whereas, monophasic, uniformly sized, nano-lath shaped particles with high aspect ratio >10 are obtained when morphology-controlling cation additives such as Pt 4+, Pd 2+ or Rh 3+ are present in FeCl 2 ( RCl≥8) solution. Preferential adsorption of additives on ( 0k0) and ( h00) planes limits the growth in the perpendicular directions leading to high aspect ratios. The effect of these additives are suppressed by the phosphate ion, a strong complexing ligand, giving rise to fibrous aggregate with the length of individual particles as small as 10-30 nm. While most of the Cl − ion is removed from the final precipitates on washing, phosphate remained as HPO 42− as evidenced from IR absorption spectra. Maghemite obtained by dehydroxylating γ-FeOOH contains randomly distributed micropores bringing in the relaxation effects of spins on the surface atoms as deciphered from Mössbauer spectroscopy. This leads to the low σs (44-48 emu/g) and Hc (120-130 Oe) for γ-Fe 2O 3−δ particles. Whereas nearly pore-free single crystalline particles obtained by reduction followed by reoxidation has high value of σs (73 emu/g) and Hc (320 Oe), which decreases to 30 emu/g and 75 Oe, respectively, for nanoparticles obtained from phosphate stabilized lepidocrocite. The mobility of iron ions and counter mobility of vacancies during the topotactic transformation of γ-FeOOH to magnetite to γ-Fe 2O 3−δ renders the particles pore-free. 相似文献
17.
The corrosion of a carbon steel was studied in different atmospheres at sites in the Republic of Panama. The weight loss (corrosion penetration) suffered by the carbon steel is related to time by a bilogarithmic law. Mössbauer spectroscopy indicated the rust was composed of non-stoichiometric magnetite (Fe 3-xO 4), maghemite (γ-Fe 2O 3), goethite (α-FeOOH) of intermediate particle size, lepidocrocite (γ-FeOOH) and superparamagnetic particles. Magnetite formation is related to the alternating dry--wet cycles. Goethite is related to corrosion penetration by a saturation type of behavior, following a Langmuir type of relationship. Goethite in rust protects steel against further atmospheric corrosion. 相似文献
18.
A complex study of the hydrogen reduction of nanosized iron hydroxide Fe(OH) 3 at 400°C was performed. It was shown that, during the reduction of Fe(OH) 3 to iron metal α-Fe, intermediate compounds such as Fe(OH) 2, α-FeOOH, β-FeOOH, γ-FeOOH, δ-FeOOH, and FeO are formed along with stable iron oxides α-Fe 2O 3, γ-Fe 2O 3, and Fe 3O 4. A scheme of chemical and structural transformations that occur in the reduction of nanosized Fe(OH) 3 is presented. The scheme takes into account the possibility of the bifurcation mechanism of reaction development. 相似文献
19.
Magnetite polycrystalline films are grown by variously oxidizing a Fe film on the Si(111) surface covered by a thin (1.5 nm)
SiO 2 layer. It is found that defects in the SiO 2 layer influence silicidation under heating of the Fe film. The high-temperature oxidation of the Fe film results in the formation
of both Fe 3O 4 and iron monosilicide. However, the high-temperature deposition of Fe in an oxygen atmosphere leads to the growth of a compositionally
uniform Fe 3O 4 film on the SiO 2 surface. It is found that such a synthesis method causes [311] texture to arise in the magnetite film, with the texture axis
normal to the surface. The influence of the synthesis method on the magnetic properties of grown Fe 3O 4 films is studied. A high coercive force of Fe 3O 3 films grown by Fe film oxidation is related to their specific morphology and compositional nonuniformity. 相似文献
20.
β-FeOOH nanoparticles have been prepared in a microemulsion system with nonionic surfactant polyoxyethylene(4)nonylphenylether CH 3(CH 2) 8C 6H 4O(CH 2OCH 2) 4H. The powder X-ray diffraction, infrared spectra, and transmission electron microscopic images indicate that the products are 20–30 nm length nanorods with a crystal structure belonging to monoclinic β-FeOOH and lattice parameters of a=0.9981, b=0.2948, c=1.0485 nm and β=92.26°. The size and shapes of β-FeOOH nanoparticles can be manipulated by the surfactant. The modified β-FeOOH nanoparticles are paramagnetic at room temperature and may be antiferromagnetic or weakly ferrimagnetic at lower temperatures. The 57Fe Mössbauer spectra show that the magnetic structure transforms below 150 K and two kinds of Fe–O octahedra exist in the lattice of the modified β-FeOOH nanoparticles. The numbers of each kind of Fe–O octahedra are not the same at room temperature or at low temperatures. 相似文献
|